1. Field of the Invention
The present invention relates to an on-board navigation apparatus and more particularly, an on-board navigation apparatus designed to display, at a display device (referred to as a display hereinafter), pictures including map information on the basis of the position of the vehicle itself
2. Description of Background Information
On-board navigation apparatuses have been introduced for practical use, in which map information is previously stored in memory, and retrieved from memory for display into a display device together with a current position of the vehicle, so that the vehicle is navigated to a predetermined destination.
The display of map information by such on-board navigation apparatuses is generally performed as follows Map information to be displayed is previously stored in a storage medium, e.g. a CD-ROM, and particular map information is read-out and loaded into a buffer memory prior to being transferred to the display device Map data is retrieved from the CD-ROM according to the type of data, and is formed by loading into the buffer memory geographical data representing the shape of roads, rivers, mountains, buildings, and so on, and name data for indicating the name of corresponding items The geographical data and name data are superimposed with each other so that the map data is drawn in the buffer memory. Otherwise, the name data may be included as a part of the map data of a single type prepared in the CD-ROM, so that the name data can by displayed by using such map data.
FIG. 2 shows an example of a display of roads as geographical data and corresponding names as name data on the display. The north direction of the map is normally displayed on the display. More particularly, the manner of display in this case is that the upward direction of the display screen d corresponds to the north direction on the map. Each road shown by a bold line is accompanied with its name, e.g. route 1 (when the road name is expressed in Japanese language, Kanji characters of, e.g. 1 meaning "national highway route 1", may be used). These letters or characters representing the road name are arranged either downward from top to bottom in the case of vertical writing, or horizontally from left to right in the case of horizontal writing.
However, if the map data shown in FIG. 2 is rotated so that the upward direction of the display screen corresponds to the east direction, the road names assigned to each road also become rotated correspondingly as shown in FIG. 3. As the result, difficulty in reading will be experienced by a viewer who is monitoring name information in the map information, as there can be cases where the characters should be read in an inverse order, or each letter or character should be rotated by 90.degree., for example, to form proper image of the road name. In particular, it is especially difficult for a driver to recognize such characters not arranged in proper order or orientation in the display screen.